1. Field of the Invention
The present invention relates to a liquid crystal display and a method of driving the same.
2. Discussion of the Related Art
Active matrix type liquid crystal displays display a moving picture using a thin film transistor (TFT) as a switching element. The active matrix type liquid crystal displays have been implemented in televisions as well as in display devices in portable devices, such as office equipment and computers, because of the thin profile of the active matrix type liquid crystal displays. Accordingly, cathode ray tubes (CRT) are being rapidly replaced by the active matrix type liquid crystal displays.
If a DC voltage is applied to a liquid crystal layer of a liquid crystal display for a long time, ions in the liquid crystal layer are polarized based on polarities of the liquid crystals. Further, as time passes, the amount of ions accumulated in the liquid crystal layer increases. An increase in the amount of accumulated ions degrades an alignment layer and alignment characteristics of the liquid crystals. In other words, the application of the DC voltage to the liquid crystal layer for a long time causes stains on the display screen, and the size of the stains increases as time elapsed. To solve the stain problem, a liquid crystal material with a low dielectric constant has been developed, or a method for improving an alignment material or an alignment method has been attempted. However, it takes a long time and a great expense to develop a material used in the method. Further, the use of the liquid crystal material with the low dielectric constant may reduce drive characteristics of the liquid crystal. According to the experimental findings, as the amount of impurities ionized inside the liquid crystal layer increases and an acceleration factor becomes large, an appearance time of the stains becomes more rapid. The acceleration factor may include temperature, time, a DC drive of the liquid crystal, and the like. For example, when a period during which a DC voltage of the same polarity is applied to the liquid crystal layer becomes longer at a high temperature, the stains worsen and the appearance time of the stains becomes rapider. Because the stains non-uniformly appear between display panels manufactured through the same manufacture line, the stain problem cannot be solved only a development of new material or an improvement of process.